My partner has recently expressed interest in being involved with another person. We talked about it, set some boundaries, and now I feel awful. Can anyone give me advice or reassurance or a smack upside the head?

I've been with my partner for 6 years. We were actively poly when we first met and were involved (introduced by a mutual partner) but have not had any other partners/dates/whatever since we got serious, 5 or so years ago.

My partner told me she was really attracted to someone, told me about it, and asked that we discuss the status of our relationship. We did and I initially told her that I was fine with her "making out" but that I wasn't comfortable with anymore than that and she said ok. I felt really horrible about it tho. I don't have any good reason to limit her. So we talked about it again and I told her it was ok if she had a sexual relationship with the person and we agreed on some ground rules (for lack of a better word).

But again, I feel horrible. I don't understand why I feel so awful about this. I'm definitely scared and anxious but if I excluded things from my life that made me scared and anxious, I'd never leave the house. I trust my partner and I have no reason to think this will negatively effect our relationship.

I don't know what to do. I want to tell her I changed my mind and that I don't want to be poly anymore but that isn't going to change things or make me feel better. What I really want to do is stick my head under the pillow and pretend like none of this happened. I don't want to deal with this but obviously that's not a reasonable or realistic scenario.